Python集合

Posted 2021-01-01 _小溢

 

　　1.集合

  1 ‘‘‘
  2 集合：可变数据类型，里面存的元素必须是不可变数据类型。
  3      集合无序，里面的元素不能重复。将列表转换为集合在转换为集合就将有重复元素的list去重了。
  4      集合{}
  5 ‘‘‘
  6 
  7 # 创建一个集合
  8 set1 = set({1, 2, 3})
  9 print(set1)     # {1, 2, 3}
 10 
 11 # 第二种创建一个集合的方法
 12 set2 = {1, 2, 3}
 13 
 14 print(set2, type(set2))     # {1, 2, 3} <class ‘set‘>
 15 
 16 # set2 = {1, 2, 3, [4, 5], {‘name‘ : ‘alex‘}}     # 报错
 17 
 18 # print(set2)
 19 
 20 
 21 # 增
 22 
 23 set1 = {‘alex‘, ‘wusir‘, ‘ritian‘, ‘egon‘, ‘barry‘}
 24 
 25 # 增，使用add
 26 set1.add(‘python‘)
 27 print(set1)     # {‘ritian‘, ‘python‘, ‘wusir‘, ‘egon‘, ‘alex‘, ‘barry‘}
 28 
 29 # 不能有重复元素
 30 set1 = {‘alex‘, ‘wusir‘, ‘ritian‘, ‘egon‘, ‘barry‘, ‘alex‘}
 31 print(set1)     # {‘wusir‘, ‘barry‘, ‘egon‘, ‘ritian‘, ‘alex‘} 自动去重
 32 
 33 
 34 # 增 update，迭代的增加
 35 
 36 set1.update(‘abc‘)
 37 
 38 print(set1)     # {‘egon‘, ‘b‘, ‘barry‘, ‘a‘, ‘wusir‘, ‘c‘, ‘ritian‘, ‘alex‘}
 39 
 40 
 41 
 42 set1 = {‘alex‘, ‘wusir‘, ‘ritian‘, ‘egon‘, ‘barry‘, ‘alex‘}
 43 
 44 # 删
 45 
 46 # 删 随机删除，返回值就是删除的那一个
 47 print(set1.pop())   # alex
 48 
 49 print(set1)     # {‘alex‘, ‘egon‘, ‘ritian‘, ‘barry‘}
 50 
 51 
 52 set1 = {‘alex‘, ‘wusir‘, ‘ritian‘, ‘egon‘, ‘barry‘, ‘alex‘}
 53 # 删，按元素删除, 没有要删的元素会报错
 54 
 55 set1.remove(‘alex‘)
 56 
 57 print(set1)     # {‘wusir‘, ‘egon‘, ‘ritian‘, ‘barry‘}
 58 
 59 # 删，清空
 60 
 61 set1.clear()
 62 
 63 print(set1)     # set() 表示空集合
 64 
 65 # 删，删除整个集合
 66 
 67 # del set1
 68 
 69 
 70 # 没有改，因为集合里面存的内容是不可变的
 71 
 72 set1 = {‘alex‘, ‘wusir‘, ‘ritian‘, ‘egon‘, ‘barry‘, ‘alex‘}
 73 # 查
 74 for i in set1:
 75     print(i)
 76 
 77 # 交集
 78 set1 = {1, 2, 3, 4, 5}
 79 set2 = {4, 5, 6, 7, 8}
 80 
 81 print(set1 & set2)      # {4, 5}
 82 print(set1.intersection(set2))      # {4, 5}
 83 
 84 
 85 # 并集
 86 set1 = {1, 2, 3, 4, 5}
 87 set2 = {4, 5, 6, 7, 8}
 88 
 89 print(set1 | set2)      # {1, 2, 3, 4, 5, 6, 7, 8}
 90 print(set2.union(set1))     # {1, 2, 3, 4, 5, 6, 7, 8}
 91 
 92 
 93 # 反交集
 94 set1 = {1, 2, 3, 4, 5}
 95 set2 = {4, 5, 6, 7, 8}
 96 
 97 print(set1 ^ set2)      # {1, 2, 3, 6, 7, 8}
 98 print(set1.symmetric_difference(set2))      # {1, 2, 3, 6, 7, 8}
 99 
100 # 差集 set1 - set2 得到set1独有的
101 set1 = {1, 2, 3, 4, 5}
102 set2 = {4, 5, 6, 7, 8}
103 
104 print(set1 - set2)      # {1, 2, 3}
105 print(set1.difference(set2))    # {1, 2, 3}
106 
107 # 子集与超集  set1 < set2 为True，则set1是set2的子集。set1 > set2 为True，则set1是set2的超集
108 set1 = {1, 2, 3}
109 set2 = {1, 2, 3, 4, 5, 6}
110 
111 print(set1 < set2)      # True
112 print(set1.issubset(set2))      # True
113 
114 print(set1 > set2)      # False
115 
116 
117 
118 
119 # 面试题：使用集合将list去重
120 li = [1, 22, 33, 22, 44, 55, 33]
121 
122 li = list(set(li))      # set后返回的是集合set类型，需要强转成list
123 
124 print(li)   # [1, 44, 55, 22, 33]
125 
126 
127 
128 # 集合本身是可变数据类型，但是内部元素是不可变数据类型
129 # 如何将集合变为不可变集合，使用frozenset让集合变为不可变集合，frozenset是不可变集合数据类型，也是无序的
130 
131 s = frozenset(‘python‘)
132 print(s)        # frozenset({‘o‘, ‘t‘, ‘p‘, ‘h‘, ‘n‘, ‘y‘})
133 
134 s1 = {1, 2, 3}
135 s2 = frozenset(s1)
136 print(s1, type(s1))     # {1, 2, 3} <class ‘set‘>
137 print(s2, type(s2))     # frozenset({1, 2, 3}) <class ‘frozenset‘>
138 
139 # frozenset集合，不能增加和删，只能查，只读集合
140 for i in s2:
141     print(i)

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